Particularly near the end of the vid
reversing at speed that’s the only downfall with the light steering on m.a.n’s . 
It seems to be throwing over more onto the right so I’m guessing he may have had a blowout or mechanical fault like a bag burst on that side of the trailer but for some reason the driver didn’t seem to have noticed it.
You’re following behind in your car, what do you do?
A. Hang back to watch the fun
B. Get past before he blocks the road.
iguana:
Particularly near the end of the vid
Drive is doing that deliberately so his mate behind can get some YT footage. You can clearly see him snaking the prime mover left and right to make the tail “wag”. Nothing to see here, move along people.
TiredAndEmotional:
You’re following behind in your car, what do you do?A. Hang back to watch the fun
B. Get past before he blocks the road.
Definitely hang back,hope he doesn’t lose it before the next exit and find an alternative route. 
Rob K:
iguana:
Particularly near the end of the vidDrive is doing that deliberately so his mate behind can get some YT footage. You can clearly see him snaking the prime mover left and right to make the tail “wag”. Nothing to see here, move along people.
Good work, inspector 
Obviously bored out of his skull.
Id have thought it could just as easily be a genuine "tail wagging the dog"? Tractor unit loaded right on the back of an extended drag, with all the weight of the engine and cab behind the axles. Ive seen them swinging around before now without anyone filming them.